F (as fabricated)
Extruded bar with no guaranteed properties, used as forging stock. The forged part is then heat treated to T6.
Low-expansion, wear-resistant bar
4032 Aluminium Round Bar
4032 is a wrought aluminium alloy with about 12 % silicon plus magnesium, copper and nickel, giving low thermal expansion, high wear resistance and good strength at elevated temperature. It is the standard material for forged pistons in road and endurance engines, and for wear parts such as compressor scrolls, valve bodies and bushings. Metline supplies 4032 round bar as forging stock and in heat-treated T6 / T651 for machining, certified to AMS 4319, ASTM B247 or EN 573-3, worldwide.
- Alloy
- 4032 (Al-Si12-Mg-Cu-Ni)
- Tempers
- F, O, T6, T651
- Thermal expansion
- ≈19.4 µm/m·°C, about 16 % below 6061
- Standards
- AMS 4319 · ASTM B247 · EN 573-3
What is 4032 aluminium?
4032 is unusual among wrought alloys: its silicon content of 11 – 13.5 % is close to that of casting alloys, yet it is cast as billet, extruded into bar and forged. Most 4xxx alloys are filler or brazing metals; 4032 is the one heat-treatable 4xxx alloy used for structural parts.
The high silicon content forms a dispersion of hard silicon particles in the matrix. These particles do three useful things. They lower the coefficient of thermal expansion to about 19.4 µm/m·°C, compared with 23 – 24 for most other aluminium alloys. They raise wear and scuff resistance, so sliding surfaces such as piston skirts can run against cast-iron or coated bores. And together with nickel, they help the alloy keep its strength and dimensional stability as it heats up.
Magnesium and copper make 4032 heat treatable: solution treatment, quench and artificial ageing to T6 give a tensile strength of about 380 MPa, comparable to 6061-T6 but with much better behaviour hot. The trade-off is lower ductility and toughness than low-silicon alloys such as 2618, which is why piston designers weigh the two alloys carefully.
4032 chemical composition (wt %)
Limits per the Aluminum Association registration and EN 573-3 (EN AW-4032, AlSi12,5MgCuNi). The AMS 4319 title gives the nominal composition as 12.2 Si, 1.0 Mg, 0.90 Cu and 0.90 Ni.
| Element | Limit (%) | Role |
|---|---|---|
| Silicon (Si) | 11.0 – 13.5 | Hard particles: low expansion and wear resistance |
| Iron (Fe) | 1.0 max | Impurity; forms intermetallics |
| Copper (Cu) | 0.50 – 1.3 | Precipitation strengthening |
| Magnesium (Mg) | 0.8 – 1.3 | Forms Mg2Si for heat-treatment response |
| Chromium (Cr) | 0.10 max | Impurity |
| Nickel (Ni) | 0.50 – 1.3 | Heat-stable intermetallics; elevated-temperature strength |
| Zinc (Zn) | 0.25 max | Impurity |
| Others, each / total | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder |
The size and distribution of the primary silicon particles matter as much as the chemistry. Fine, evenly spread silicon gives better forging behaviour, fatigue strength and machined finish, so piston forgers often set microstructure requirements on the bar.
4032 mechanical and physical properties
Typical values from Aluminum Association / ASM data for 4032-T6. Specified minimums are lower: ASTM B247, for example, sets a tensile minimum of about 360 MPa for 4032-T6 die forgings, and AMS 4319 sets its own minimums for T651 bar. Use the governing specification and certificate for design.
| Property | 4032-T6 (typical) | Notes |
|---|---|---|
| Tensile strength | 380 MPa / 55 ksi | Similar to 6061-T6 at room temperature |
| Yield strength (0.2 %) | 315 MPa / 46 ksi | |
| Elongation | about 9 % | Forgings and large bar can be lower |
| Hardness | about 120 HB | |
| Shear strength | about 260 MPa / 38 ksi | |
| Fatigue strength (5×10⁸ cycles) | about 110 MPa / 16 ksi | Rotating beam |
Physical properties (T6, typical)
- Density
- 2.68 g/cm³ (0.097 lb/in³)
- Melting range
- about 532 – 571 °C
- Modulus of elasticity
- about 79 GPa (11,400 ksi), higher than most alloys due to silicon
- Coefficient of thermal expansion
- about 19.4 µm/m·°C (20 – 100 °C)
- Thermal conductivity
- about 140 – 155 W/m·K
- Electrical conductivity
- about 34 – 35 % IACS
The modulus is worth noting: at about 79 GPa, 4032 is roughly 10 % stiffer than 6061, which helps ring lands and thin walls resist deflection.
4032 tempers explained
O (annealed)
Softened for machining or forming before final heat treatment. Rarely used in service.
T6
Solution treated at about 505 – 515 °C, quenched and artificially aged at roughly 170 – 175 °C. The standard service condition for pistons and wear parts.
T651
T6 plus stress relief by stretching. Preferred for bar that will be machined, because it moves less when material is removed. Covered by AMS 4319.
Elevated-temperature tempers
Some piston makers use stabilising or over-ageing treatments so dimensions stay stable at operating temperature. Agree these with the forger.
Choosing a temper
Order F for forging stock and T651 or T6 for parts machined directly from bar.
4032 standards and international equivalents
| System | Designation | Typical standards |
|---|---|---|
| Aerospace (SAE) | 4032-T651 | AMS 4319 (rolled or cold finished bar and rod, 0.750 – 3.500 in) |
| Aluminum Association / ASTM | 4032 | ASTM B247 (die and hand forgings, T6) |
| UNS | A94032 | — |
| European (EN) | EN AW-4032 / AlSi12,5MgCuNi | EN 573-3 (chemistry); EN 586 (forgings) |
| Japan (JIS) | A4032 | JIS H4040 (bar), JIS H4140 (forgings) |
| GB | 4032 (4A11 similar) | GB/T 3190, GB/T 3191 |
4032 is a specialised alloy and is not listed in every bar standard, so commercial bar is often certified to AMS 4319, to EN 573-3 chemistry with agreed properties, or to a customer specification. 4A11 is a closely related forging alloy; confirm acceptance before substituting it. The old AMS 4145 forging specification for 4032 has been cancelled; check the current revision of any specification cited on older drawings.
4032 bar sizes and weights
| Form | Typical range | Condition | Main use |
|---|---|---|---|
| Extruded round bar (forging stock) | Common piston-stock diameters, about 50 – 150 mm | F | Forged pistons and wheels |
| Cold-finished / rolled round bar | About 19 – 89 mm (AMS 4319 range); other sizes by agreement | T6, T651 | Machined pistons, bushings, valve parts |
| Larger extruded bar | Larger diameters on request | F, T6 | Compressor scrolls, large wear parts |
| Saw-cut slugs | Cut to forging weight | F | Ready-to-forge piston blanks |
| Square, flat and hex bar | On request | T6, T651 | Wear plates and fittings |
Bars are supplied in random or fixed lengths, or cut to size. Weights for solid round 4032 bar at 2.68 g/cm³:
| Diameter (mm) | kg per metre | 3 m bar (kg) | 6 m bar (kg) |
|---|---|---|---|
| 20 | 0.842 | 2.53 | 5.05 |
| 25 | 1.32 | 3.95 | 7.89 |
| 30 | 1.89 | 5.68 | 11.37 |
| 40 | 3.37 | 10.10 | 20.21 |
| 50 | 5.26 | 15.79 | 31.57 |
| 60 | 7.58 | 22.73 | 45.47 |
| 70 | 10.31 | 30.94 | 61.88 |
| 80 | 13.47 | 40.41 | 80.83 |
| 90 | 17.05 | 51.15 | 102.30 |
| 100 | 21.05 | 63.15 | 126.29 |
| 110 | 25.47 | 76.41 | 152.81 |
| 120 | 30.31 | 90.93 | 181.86 |
| 130 | 35.57 | 106.72 | 213.43 |
| 150 | 47.36 | 142.08 | 284.16 |
4032 versus 2618 for forged pistons
Almost all forged pistons are made from either 4032 or 2618. The choice depends on how hard the engine will be used and how much cold clearance and noise are acceptable.
| Factor | 4032 | 2618 / 2618A |
|---|---|---|
| Silicon content | High (≈12 %) | Very low (≈0.2 %) |
| Thermal expansion | ≈19.4 µm/m·°C | ≈22 – 23 µm/m·°C |
| Piston-to-bore clearance | Tighter; quieter cold starts | Larger; some cold slap |
| Wear and scuff resistance | Very good | Good, often coated |
| Ductility and toughness | Lower | Higher; tolerates detonation |
| Ring-groove stability | Very good over long service | Good; grooves may need anodising |
| Density | 2.68 g/cm³ | 2.76 g/cm³ |
| Typical use | Street performance, endurance, OEM-style forged pistons | Racing, high boost, nitrous, heavy-duty |
In practice, 4032 suits engines that run long hours with moderate power gains, where tight clearances, low noise and long ring life matter. For extreme cylinder pressures or detonation risk, 2618 is the safer choice.
Forging, machining, welding and finishing
Forging
Forge at roughly 415 – 460 °C with heated dies. The alloy is less ductile than 6xxx or 2xxx grades, so control die temperature and reduction per blow to avoid cracking.
Machining
Silicon particles are abrasive. Use polished carbide or, for production runs, PCD tooling with positive rake, high speeds and moderate feeds. Keep coolant clean to protect the finish.
Heat treatment
Leave allowance for distortion during quenching, then check size and straightness and take a finishing cut. T651 bar minimises movement during machining.
Welding
Weldable with 4043 or 4047 filler, which matches its silicon level; high-magnesium fillers should be avoided. Laser welding is used on housings. Most pistons are not welded.
Anodising and coatings
High silicon gives a dark grey anodic film. Hard anodising of ring grooves and skirt coatings are common on pistons.
Corrosion
Fair to good. Pistons operate in oil; exposed parts are usually anodised or coated.
Do not machine 4032 with uncoated HSS tools for production work; tool wear is rapid and surface finish deteriorates quickly.
Where 4032 round bar is used
- Engines: forged pistons for performance road cars, motorcycles, small aircraft and endurance engines
- Compressors: scroll compressor parts, swash plates and pistons in automotive air-conditioning compressors
- Automotive hydraulics: brake master-cylinder parts, transmission valve bodies and spools
- Bearings and bushings: steering bushings, wear sleeves and sliding parts
- Precision equipment: parts that must hold dimensions with temperature change, such as instrument and copier components
- Housings: laser-welded enclosures that need low distortion and stable dimensions
4032 compared with 2618, 6061 and 2024
| Property | 4032-T6 | 2618-T61 | 6061-T6 | 2024-T4 |
|---|---|---|---|---|
| Typical tensile strength | 380 MPa | 440 MPa | 310 MPa | 469 MPa |
| Thermal expansion (µm/m·°C) | 19.4 | ≈22.3 | 23.6 | 23.2 |
| Wear resistance | Very good | Good | Fair | Fair |
| Elevated-temperature strength | Good | Excellent | Poor | Fair |
| Ductility | Low – moderate | Moderate | Good | Good |
| Density (g/cm³) | 2.68 | 2.76 | 2.70 | 2.78 |
4032 is the right pick where low thermal growth and wear resistance drive the design. For machined structural parts at room temperature, 6061 or 2024 are easier to machine and more ductile.
How to order 4032 round bar from Metline
- SpecifyAlloy 4032, temper (F for forging stock, T6 or T651 for machining), diameter, length or slug weight, and quantity.
- Confirm the standardAMS 4319, ASTM B247 (for forgings), EN 573-3 chemistry or your own specification, plus any microstructure, ultrasonic or hardness requirement.
- QuoteWe confirm availability, tolerance class, certification and delivery terms (EXW, FOB, CIF or DAP) for your destination port or site.
- Process and inspectBar is cut to length or slug weight, checked for diameter, straightness and surface, and ultrasonically tested where required.
- Document and shipEach lot ships with an EN 10204 3.1 mill test certificate and packing list. Bars are bundled or cased in seaworthy wooden boxes with moisture protection; third-party inspection can be arranged on request.
References and standards
- SAE AMS 4319 – Aluminum Alloy, Rolled or Cold Finished Bars and Rods, 12.2Si 1.0Mg 0.90Cu 0.90Ni (4032-T651)
- ASTM B247 – Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings
- EN 573-3 – Chemical composition and form of wrought products (EN AW-4032)
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- ASM Handbook, Vol. 2 – Properties of Wrought Aluminum and Aluminum Alloys: 4032
4032 aluminium (aluminum) round bar: frequently asked questions
Why is 4032 used for pistons?
Its high silicon content lowers thermal expansion and raises wear resistance, so pistons can run tighter bore clearances with less noise and longer ring-groove life.
Is 4032 or 2618 better for a turbocharged engine?
For moderate boost and long service, 4032 works well. For high boost, nitrous or any risk of detonation, 2618 is preferred because it is tougher and more ductile.
What temper should I order for piston forging?
Order F (as fabricated) bar or slugs. The forged piston is solution treated and aged to T6 afterwards. Order T651 if you will machine parts directly from bar.
What standard covers 4032 bar?
AMS 4319 covers 4032-T651 rolled or cold-finished bar and rod from 0.750 to 3.500 in. Forgings are covered by ASTM B247, and chemistry by EN 573-3 and the Aluminum Association registration.
Can 4032 aluminium be welded?
Yes, with 4043 or 4047 filler, and laser welding is used on housings. Avoid high-magnesium fillers. Pistons themselves are normally not welded.
Is 4032 hard to machine?
It machines to a good finish, but the silicon particles wear tools quickly. Polished carbide or PCD tooling is recommended.
Need 4032 round bar or piston stock?
Send temper, diameter, length or slug weight and specification. We will reply with availability, certification and delivered terms.
